The present invention relates to a miniaturized solid electrolyte capacitor that has integral terminals suitable for flush mounting, and more particularly to such a capacitor wherein the terminals are comprised of metal loaded resin end caps.
To make a flush mounting solid electrolyte capacitor, it is known to fit a plastic sleeve over a solid tantalum capacitor, and thereafter to fit cup shaped metal end caps to the two ends of the capacitor over the sleeve. Such a construction is described by Millard et al in U.S. Pat. No. 3,828,227, issued Aug. 6, 1974. An anode riser wire is welded to the anode end cap while the cathode end cap is connected to the counterelectrode of the body by means of a conductive epoxy. Another construction is taught by Markarian in U.S. Pat. No. 3,795,844 issued Mar. 5, 1974 wherein a solid tantalum capacitor section is inserted into an insulated metal tube. Metal terminal layers are provided over the insulation of each end of the tube. Conductive epoxy or solder plugs make the connection between the terminals and the anode and cathode, respectively. Both patents are assigned to the same assignee as the present invention. Both of these constructions offer a highly disciplined geometry and the capability for withstanding severe reflow soldering conditions. However, other capacitor applications call for even lower costs and high volume efficiency.
Another similar construction employs an insulative coating of tetrafluorethylene over the body, and sheet metal end caps are connected by means of a conductive adhesive. The anode riser wire is welded to one of the end caps. Yet another similar capacitor intended for spring clip mounting is described by Fournier in U.S. Pat. No. 3,341,752 issued Sept. 12, 1967, also assigned to the same assignee, wherein the capacitor body having a cathode and anode wire is contained within a plastic tube, the tube filled with an insulative resin and conductive coatings at each end connect to the anode and cathode wires and form clipable terminations.
The above constructions either have less than an optimum volume efficiency as measured by the volt-microfarad product per unit package volume, or require metal end caps to be fitted over the ends of the capacitor with which there are associated problems of cost and reliability. Fitted end caps of the proper size must be provided for each capacitor body size and even for one body size, dimensional control must be maintained to assure a proper fit. Also, it is desirable to eliminate all voids under the fitted end cap to avoid trapping flux or other contaminants and corrosive materials in such voids. Attempts to accomplish this by back filling the end cap with epoxy or the like are painstaking and then not always fully effective. Furthermore, the bimetallic weld between the tantalum anode riser wire and the solderable fitted end cap is subject to fracture in thermal shock or mechanical stress and is a potential source of early failure.
It is therefore an object of the present invention to provide a low cost solid electrolyte valve-metal capacitor suitable for flush mounting.
It is another object of the present invention to provide such a capacitor having high volume efficiency and high reliability.
It is a further object of this invention to provide such a capacitor that can be made by process steps of a minimum number and of a simple noncritical nature.
It is a further object of this invention to provide such a capacitor that can be made by process steps that do not tend to produce flux trapping voids and that do not include welding.
It is yet a further object of this invention to provide such capacitors that can be made by process steps most of which can be executed on a multiple basis.